This invention relates to anode members in electric discharge apparatus generally and in gas lasers in particular.
It is usual for the anodes and cathodes of electric discharge apparatus to be non-porous, but it has also been proposed to provide an apertured electrode in certain kinds of electric discharge apparatus, for example plasma torches, to facilitate cooling of the electrode; a cool stream of gas is passed through the interior of the electrode and emerges through its surface.
One of the objects commonly applicable in the design of a gas laser is that of achieving with reliability ability the maximum power output from a given physical size of laser. Another consideration is the efficiency of the laser.
In a typical high power gas laser, a reflective and partially reflective mirror define an optical path within the laser cavity. A glow discharge is generated in the laser cavity between electrodes to provide plasma in the cavity and the gas is circulated around a closed path which incorporates the laser cavity. The glow discharge that is generated may be approximately aligned with the optical axis in the cavity as in an axial flow laser or it may be transverse to the optical axis as in a transverse-discharge laser. Furthermore, the discharge may be generated from an alternating voltage source or from a pulsed direct voltage source to provide an intermittent discharge as in a pulsed laser or the discharge may be generated from a direct voltage source to provide a continuous laser output. One limitation of the power output that can be obtained in a laser arises from the fact that as the discharge current is increased so there is a tendency for a glow discharge to change to an arc (glow to arc transition). One region where such a transition is likely to occur is the anode region and it is therefore desirable to provide a gas laser in which the possibility of glow to arc transition occurring in the anode region is reduced.
In the February 1970 issue of the IEEE Journal of Quantum Electronics a transverse-discharge gas laser is described in which discharges are generated between a plurality of anodes and cathodes, the discharges extending perpendicular to the optical axis of the laser. The discharges generated between respective electrodes are spaced apart from one another sufficiently to prevent coalescing of the discharges. In order to improve the laser gain gas is injected through the anodes which are in the form of open ended tubes. We have found that with an arrangement of this kind, a discharge from an anode seats on an exterior edge of the tube and is therefore outside the flow of gas through the tube.
It is an object of the invention to provide a gas laser having at least one anode member and which is able to provide a high output power for a given size of laser, with the anode member arranged so as to inhibit the generation of arcs in the anode region.